Catheters for the introduction or removal of fluids may be located in various venous locations and cavities throughout the body for introduction or removal of these fluids. Such catheterization may be performed by using a single catheter having multiple lumens. A typical example of a multiple lumen catheter is a dual lumen catheter in which one lumen introduces fluid and the other lumen removes fluid. An example of such multiple lumen catheter is the SPLIT-CATH® catheter.
Generally, to insert any catheter into a blood vessel, the vessel is identified by aspiration with a long hollow needle in accordance with the well known Seldinger technique. When blood enters a syringe attached to the needle, indicating that the vessel has been found, a thin guide wire is then introduced, typically through a syringe needle or other introducer device into the interior of the vessel. The introducer device is then removed, leaving the guide wire within the vessel. The guide wire projects beyond the surface of the skin. At this point, several options are available to a physician for catheter placement. The simplest is to pass a catheter into the vessel directly over the guide wire. The guide wire is then removed, leaving the catheter in position within the vessel. However, this technique is only possible in cases where the catheter is of a relatively small diameter, made of a stiff material, and not significantly larger than the guide wire, for example, for insertion of small diameter dual lumen catheters. If the catheter to be inserted is significantly larger than the guide wire, a dilator device is passed over the guide wire to enlarge the hole. The catheter is then passed over the guide wire, and the guide wire and dilator are then removed.
Several different designs of dual lumen catheters are known. One design incorporates side-by-side lumens in which one lumen (the arterial lumen) draws fluid from the body and the other lumen (the venous lumen) delivers fluid to the body. The venous lumen is typically longer than the arterial lumen to reduce recirculation of the fluid. One drawback of the side-by-side catheter is the fact that, during use, the suction effect of the arterial lumen occasionally draws the side wall of the vessel into which the catheter is inserted against the lumen, effectively reducing the ability of fluid to flow into the catheter.
An alternative design is a coaxial design, such as is disclosed in U.S. Pat. No. 5,480,380. In such a catheter design, the arterial lumen is peripheral to the venous lumen, which extends along the longitudinal axis of the catheter. Like the side-by-side catheter, the venous lumen in the coaxial catheter is typically longer than the arterial lumen to reduce recirculation. One problem with this design is that the inlet openings on the arterial lumen are on the sides of the lumen. The most proximal opening is typically the only opening that receives heparin or other anti-clotting agent in between treatments, allowing the remaining openings to clot. Also, the suction effect of the arterial lumen may draw the lumen against the side wall of the vessel, reducing the available surface area of the openings, thereby restricting flow into the lumen.
It would be beneficial to provide a coaxial catheter that reduces the potential for a suction effect of the arterial lumen against a vessel wall, and maximizes the amount of fluid that may be taken in by the lumen during catheter operation.